I have been over on the Benz world forum and there is a guy with a W123 that said he keeps frying alternators even when they are replaced.

I can't remember if a bad ground would cause his issue or not. If you have a reason post here and I will post the answer on benzworld or go to his thread and comment.

https://www.benzworld.org/threads/alternator-woes.3041438/

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84 300D, 82 Volvo 244Gl Diesel